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How to see infrared rays. Infrared light - a workshop of invisibly warm radiation. Wavelength and frequency range of infrared radiation

How to see infrared light

In a laser, a photon of light colliding with an excited atom of the medium stimulates the emission of another photon of the same frequency. Secondary photons, in turn, cause the emission of photons by other excited atoms - as a result, the process of light emission proceeds like an avalanche. But let us try to consider the case when the active medium of the laser is in a subcritical state, i.e., too rarefied to support the avalanche-like process. In such a medium, a photon can collide with an unexcited atom, which, having absorbed this photon, passes into an excited state. Another photon, colliding with this excited atom, can now stimulate emission, and the two photons will move together, in pairs. In a somewhat denser medium and with slightly more intense pumping, this pair of photons can collide with another excited atom, resulting in a photon triplet. In general, the active medium of the laser leaves about the same number of photons as entered it, but the outgoing photons form coherent pairs and triplets.

This "grouped" light has amazing properties. First of all, it is completely unfamiliar to the eye. Thus, the red grouped light will reflect off red objects in the usual way. But, since each pair of "red" photons has a sum of energy equal to the energy of one "blue" photon, such light, due to two-photon absorption, will also excite receptors that are sensitive to blue. Thus, the object will look both red and blue at the same time, probably iridescent purple. Most of all, however, Daedalus is interested in infrared grouped light. All objects around us emit an abundance of long-wave infrared radiation. It is enough, therefore, in front of any object to place a "photon buncher" by NIGHTMAR, which collects photons into groups, the total energy of which lies in the visible region of the spectrum - and here's free lighting for you! True, in grouped IR light, all objects are likely to have an eerie appearance, so it would be better if the energy of a group of photons falls on the ultraviolet region. Then, using an ordinary phosphor, as in fluorescent lamps, it is possible to excite it through multiphoton absorption and obtain visible light. This sleek device converts useless infrared background into visible light - like a heat pump pumping heat from lower-temperature bodies to higher-temperature bodies. According to the laws of thermodynamics, these devices can take away much more energy (heat and light) from the environment than is necessary to activate them.

New Scientist,June 26, 1980

From the notebook of Daedalus

Consider an active medium in which N 1 atoms are in the ground state and N 2 are in an excited state with energy E. The operating frequency is then v \u003d E / h, and if this frequency corresponds to the energy density νv, then the excitation intensity N 1 -\u003e N 2 will be BN 1? V, where B is the transition probability. Similarly, the intensity of stimulated emission is equal to BN2? V. Let the system include n photons. For each of them, the probability of being absorbed during the transition of an atom from state 1 to state 2 is proportional to BN 1?; we denote this probability by KN 1. Then the number of photons absorbed in the system is equal to nKN 1 for small KN 1, and n (1 - KN 1) photons pass through the entire medium. The probability that each of these photons stimulates the emission of a photon by an excited atom is KN 2. Thus, the most probable number of pairs of photons emerging from the medium is n (KN 2) 1 (1 - KN 1). In other words, we let n photons into the medium and received at the output n (KN 2)? (1 - KN 1 photon pairs; thus, the efficiency of our laser for "bunching" photons is 2 / KN 2 (1 - KN 1). This value has a maximum at N 2 \u003d N 1, i.e. when the pump radiation, which transfers atoms to an excited state due to the transitions N 1 -\u003e N 3 -\u003e N 2, is slightly insufficient to create an inverse population, i.e. the system is slightly below the threshold of laser radiation generation.When KN 1 \u003d KN 2 \u003d 0.5, the maximum efficiency \u003d 0.5, that is, it can be expected that approximately half of the total number of photons entering the system will be grouped. groups of not only two, but also three or more photons, but even with this in mind, our scheme looks quite real.

How will photon pairs behave? In physical processes (refraction, scattering, etc.) they should behave in exactly the same way as generating photons, however, in chemical processes (absorption, etc.) they are likely to exhibit a tendency towards two-photon absorption, and therefore, each pair behaves like a single photon with twice the frequency. On this basis, it is probably possible to create street lamps that emit bunched infrared light that easily passes through the fog and at the same time is well perceived by the eye. How would you feel about "anti-umbrella", which converts the light of a cloudy day into ultraviolet radiation for tanning? Finally, since the bunched photons are coherent with the photon that originally entered the medium, the appropriate glasses will allow direct observation of the infrared image.

Daedalus receives a letter

Myron L. Walbarst, Professor of Ophthalmology and Biomedical Engineering, Duke University Medical Center, Durham, N. Carolina, USA July 23, 1980

Dear Ariadne!

Your friend Daedalus considered (p. 448, June 26, 1980) the use of bunched light to excite the blue receptors of the eye by two-photon absorption, and even admitted the possibility of using long-wave infrared radiation to produce visible light. I am attaching a copy of one of my published works, "The visual sensitivity of the eye to infrared radiation" ( Journal of the Optical Society of America, 66, 1976, p. 339), which shows that this is indeed possible. I hope that Daedalus will continue his research, but he should be aware that today science is moving forward so quickly that even a dreamer can lag behind life.

Yours sincerely M. Walbarsht

(In what follows, grouped light will be shed on the priority question in the article "Infrared Vision Again".)

From the book Secrets of the Moon Race author Karash Yuri Yurievich

UN Agreements: Light at the End of a Tunnel or a Dead End? "Tunnel" I didn't want the reader to get the impression that the sixties were a time of fruitless hopes, lost illusions and lost ones for Soviet-American cooperation in space.

From the book Parade of World Exhibitions author Mezenin Nikolay Alexandrovich

Paris 1878. "RUSSIAN LIGHT" In France, 1873 - 1879 as a whole was a period of crisis and decline, which was observed throughout Europe. But Marx, referring to 1878, noted that during this "year, so unfavorable for all other businesses, railways flourished; but this

From the CCTV book. The CCTV Bible [Digital & Networking] author Damianovski Vlado

2. Light and television Let there be light. A bit of history Light is one of the main and greatest natural phenomena, light is not only a necessary condition for life on the planet, but also plays an important role in technological progress and inventions in the field of visual communication:

From the book History of Outstanding Discoveries and Inventions (Electrical Engineering, Electric Power Engineering, Radio Electronics) author Schneiberg Jan Abramovich

CHAPTER 8 Human genius creates electric light, "like the sun" Yablochkov "electric candle" Creation of sources of electric lighting is one of the fundamental discoveries in the history of mankind. The first to say

I don’t know about you, but I’ve always wondered: what would the world look like if the RGB color channels in the human eye were sensitive to a different wavelength range? Rummaging through the bottom of the barrel, I found infrared flashlights (850 and 940nm), a set of IR filters (680-1050nm), a black and white digital camera (no filters at all), 3 lenses (4mm, 6mm and 50mm) designed for photography in IR light. Well, let's try to see.

We have already written on the topic of IR photography with the removal of the IR filter on Habré - this time we will have more opportunities. Also photos with other wavelengths in RGB channels (most often with IR capture) - can be seen in posts from Mars and about space in general.

These are flashlights with IR diodes: 2 left at 850nm, right at 940nm. The eye sees a faint glow at 840nm, the right one only in complete darkness. For an IR camera, they are dazzling. The eye seems to retain microscopic sensitivity to near infrared + LED radiation is at lower intensity and at shorter (\u003d more visible) wavelengths. Naturally, you need to be careful with powerful IR LEDs - if you are lucky, you can imperceptibly burn the retina (as well as from IR lasers) - the only thing that saves you is that the eye cannot focus the radiation to a point.

Black and white 5 megapixel noname USB camera - on Aptina Mt9p031 sensor. Shaking the Chinese for a long time about black and white cameras - and one seller finally found what I needed. There are no filters in the camera at all - you can see from 350nm to ~ 1050nm.

Objectives: this one is 4mm, there are still 6 and 50mm. At 4 and 6mm - designed to work in the IR range - without this, for the IR range without refocusing, the images would be out of focus (an example will be below, with a conventional camera and IR radiation of 940nm). It turned out that the C mount (and CS with a 5mm focal distance) came from 16mm cameras from the beginning of the century. Lenses are still actively produced - but already for video surveillance systems, including by well-known companies like Tamron (the 4mm lens is just from them: 13FM04IR).

Filters: I again found a set of IR filters from 680 to 1050nm from the Chinese. However, the IR transmission test gave unexpected results - it looks like not band-pass filters (as I imagined it), but rather different "density" colors - which changes the minimum wavelength of the transmitted light. Filters after 850nm turned out to be very dense and require long exposures. IR-Cut filter - on the contrary, allows only visible light to pass through, we will need it when shooting money.

Visible Light Filters:

IR filters: red and green channels - in the light of 940nm flashlight, blue - 850nm. IR-Cut filter - reflects infrared radiation, that's why it has such a funny color.

Let's start shooting

Daytime IR panorama: red channel - with a filter at 1050nm, green - 850nm, blue - 760nm. We see that trees reflect the very near infrared especially well. Colored clouds and colored spots on the ground - turned out from the movement of clouds between frames. Separate frames were combined (if there could be an accidental camera shift) and stitched into 1 color image in CCDStack2 - a program for processing astronomical photographs, where color images are often made from several frames with different filters.

Panorama at night: you can see the difference in color of different light sources: "energy efficient" - blue, visible only in the near infrared. Incandescent lamps are white, they shine in the entire range.

Bookshelf: Nearly all common objects are virtually colorless in IR. Either black or white. Only some paints have a pronounced "blue" (shortwave IR - 760nm) shade. LCD screen of the game "Just wait!" - shows nothing in the IR range (although it works for reflection).

A cell phone with an AMOLED screen: absolutely nothing is visible on it in the IR, as well as the blue indicator LED on the stand. In the background - nothing is visible on the LCD screen either. The blue paint on the metro ticket is transparent in IR - and the antenna for the RFID chip inside the ticket is visible.

At 400 degrees, a soldering iron and a hairdryer glow quite brightly:

Stars

It is known that the sky is blue due to Rayleigh scattering - accordingly, in the infrared range, it has a much lower brightness. Is it possible to see the stars in the evening or even during the day against the sky?

Photo of the first star in the evening with an ordinary camera:

IR camera without filter:

Another example of the first star in the background of the city:

Money

The first thing that comes to mind for authenticating money is UV radiation. However, banknotes have a lot of special elements that appear in the IR range, including those visible to the eye. We have already briefly written about this on Habré - now let's see for ourselves:

1000 rubles with filters 760, 850 and 1050nm: only individual elements are printed with IR-absorbing ink:

5000 rubles:

5000 rubles without filters, but with lighting at different wavelengths:
red \u003d 940nm, green - 850nm, blue - 625nm (\u003d red light):

However, infrared money tricks don't end there. The banknotes have anti-Stokes markers - when illuminated with IR light at 940nm, they glow in the visible range. Taking a photo with an ordinary camera - as we can see, the IR light passes a little through the built-in IR-Cut filter - but because the lens is not optimized for IR - the image is out of focus. Infrared light looks light purple because Bayer RGB filters are transparent to IR.

Now, if we add an IR-Cut filter, we will see only glowing anti-Stokes markers. The element above "5000" - glows the brightest, it is visible even with not bright room lighting and 4W 940nm diode / flashlight illumination. This element also contains a red phosphor - it glows for several seconds after irradiation with white light (or IR-\u003e green from an anti-Stokes phosphor of the same label).

The element slightly to the right of "5000" is a phosphor that glows green for some time after irradiation with white light (it does not require IR radiation).

Summary

Money in the IR range turned out to be extremely tricky, and you can check it in the field not only with UV, but also with an IR 940nm flashlight. The results of shooting the sky in IR - give rise to hope for amateur astrophotography without going far outside the city.

We know how to do? Nope.

We are all used to the fact that flowers are red, black surfaces do not reflect light, Coca-Cola is opaque, a hot soldering iron cannot illuminate anything like a light bulb, and fruits can be easily distinguished by their color. But let's pretend for a moment that we can see not only the visible range (hee hee), but also the near infrared. Near infrared light is not at all what you see in a thermal imager. It is closer to visible light rather than thermal radiation. But it has a number of interesting features - often completely opaque objects in the visible range are perfectly translucent in infrared light - an example in the first photo.
The black surface of the tile is transparent to IR, and with the help of the camera, from which the filter is removed from the matrix, you can see part of the board and the heating element.

For a start - a small digression. What we call visible light is just a narrow strip of electromagnetic radiation.
Here, for example, I resisted the following picture from Wikipedia:

We just don't see anything other than this small part of the spectrum. And the cameras that people make are originally castrated in order to achieve a similarity between a photograph and human vision. The matrix of the camera is able to see the infrared spectrum, but a special filter (called Hot-mirror) removes this feature - otherwise the pictures will look somewhat unusual for the human eye. But if this filter is removed ...

Camera

The subject was a Chinese phone, which was originally intended for review. Unfortunately, it turned out that his radio part is severely buggy - it either accepts or does not receive calls. Of course, I didn't write about it, but the Chinese did not want to send a replacement or take this one. So he stayed with me.
We disassemble the phone:

We take out the camera. Using a soldering iron and a scalpel, carefully separate the focusing mechanism (top) from the matrix.

There should be a thin glass on the matrix, possibly with a greenish or reddish tint. If it's not there, look at the part with the "lens". If not there, then most likely everything is bad - it is sprayed on the matrix or on one of the lenses, and removing it will be more problematic than finding a normal camera.
If it is, we need to remove it as accurately as possible without damaging the matrix. At the same time, it cracked for me, and it took a long time to blow out fragments of glass from the matrix.

Unfortunately, I lost my photos, so I'll show you a photo of irenica from her blog, who did the same thing, but with a webcam.

That shard of glass in the corner is the filter. Was filter.

Putting it all back, considering that when the gap between the lens and the sensor is changed, the camera will not be able to focus correctly - you will get either a short-sighted or a far-sighted camera. It took me three times to assemble and disassemble the camera to get the autofocus mechanism working correctly.

Now you can finally assemble your phone and start exploring this new world!

Paints and substances

Coca-Cola suddenly became translucent. Light from the street penetrates through the bottle, and even objects in the room are visible through the glass.

The cloak turned from black to pink! Well, except for the buttons.

The black part of the screwdriver also brightened. But for the phone, this fate befell only the joystick ring, the rest is covered with another paint that does not reflect IR. So does the plastic phone dock in the background.

The pills turned from green to purple.

Both chairs in the office have also gone from gothic black to incomprehensible color.

The leatherette remained black, while the fabric turned out to be pink.

The backpack (it is in the background of the previous photo) became even worse - it almost all became lilac.

As well as a camera bag. And the cover of the e-book

The stroller has turned from blue to the expected purple. And the reflective stripe, clearly visible in a conventional camera, is not at all visible in IR.

Red paint, as close to the part of the spectrum we need, reflects red light, and captures part of the IR. As a result, the red color brightens noticeably.

Moreover, all red paint that I have noticed has this property.

Fire and temperature

A barely glowing cigarette looks like a very bright dot in IR. People are standing at the bus stop with cigarettes at night - and their tips illuminate their faces.

A lighter, the light of which in a regular photo is quite comparable to the background lighting in the IR mode, blocked the pathetic attempts of street lamps. The background is not even visible in the photo - the smart camera worked out the change in brightness, reducing the exposure.

The soldering iron glows like a small light bulb when it warms up. And in the mode of maintaining the temperature it has a soft pink light. And they also say that soldering is not for girls!

The burner looks almost the same - well, except that the torch is a little further away (at the end, the temperature drops quite quickly, and at a certain stage it stops shining in visible light, but still shines in IR).

But if you heat a glass rod with a burner, the glass will begin to glow quite brightly in the IR, and the rod will act as a waveguide (bright tip)

Moreover, the stick will glow for a long time even after the heating stops

A hot air station hair dryer generally looks like a flashlight with a mesh.

Lamps and light

The letter M at the entrance to the metro burns much brighter - it still uses incandescent bulbs. But the sign with the name of the station hardly changed its brightness - it means there are fluorescent lamps.

The yard looks a little strange at night - the grass is lilac and much lighter. Where the camera can no longer cope in the visible range and is forced to increase ISO (graininess in the upper part), a camera without an IR filter has enough light with a margin.

In this photo, a funny situation turned out - the same tree is illuminated by two lanterns with different lamps - on the left with an NL lamp (orange street lamp), and on the right with an LED. The former has IR in the spectrum, and therefore the foliage underneath appears light purple in the photograph.

And LED does not have IR, but only visible light (therefore, LED lamps are more energy efficient - energy is not wasted on the radiation of unnecessary radiation, which a person will not see anyway). Therefore, the foliage has to reflect what is.

And if you look at the house in the evening, you will notice that different windows have different shades - some are bright purple, while others are yellow or white. In those apartments, whose windows are glowing purple (blue arrow), incandescent lamps are still used - the hot spiral shines evenly for everyone across the entire spectrum, capturing both the UV and IR ranges. Energy-saving lamps of cold white light (green arrow) are used in the entrances, and in some apartments - luminescent warm light (yellow arrow).

Sunrise. Just sunrise.

Sunset. Just a sunset. The intensity of sunlight is not enough for a shadow, but in the infrared range (maybe due to different refraction of light with different wavelengths, or because of the permeability of the atmosphere), shadows are clearly visible.

Interesting. In our corridor, one lamp died and the light barely, and the second did not. In infrared light, on the contrary - a dead lamp shines much brighter than a living one.

Intercom. More precisely, the thing next to him, which is with cameras and lights that turn on in the dark. It is so bright that it can be seen on a regular camera, but for infrared it is almost a spotlight.

The backlight can be turned on during the day by covering the light sensor with your finger.

CCTV lighting. The camera itself had no illumination, so they made it out of shit and sticks. It is not very bright because it was filmed during the day.

Live nature

Hairy kiwi and lime green are almost identical in color.

The green apples turned yellow and the red ones turned bright purple!

The white peppers turned yellow. And the usual green cucumbers are some kind of alien fruit.

Bright flowers have become almost monochromatic:

The flower is almost indistinguishable in color from the surrounding grass.

And the bright berries on the bush have become very difficult to see in the foliage.

What berries - even the multi-colored foliage has become monochromatic.

In short, you won't be able to choose fruits by their color. We'll have to ask the seller, he has normal vision.

But why is everything pink in the photos?

To answer this question, we will have to recall the structure of the camera matrix. I stole the picture from Wikipedia again.

This is a bayer filter - an array of filters, colored in three different colors, located above the matrix. The matrix perceives the entire spectrum in the same way, and only filters help to build a full-color picture.
But the filters transmit infrared spectrum differently - more blue and red, and less green. The camera thinks that instead of infrared radiation, ordinary light enters the matrix and tries to form a color image. In photographs where the brightness of the infrared radiation is minimal, ordinary colors still break through - in photographs you can notice color shades. And where the brightness is high, for example on the street under the bright sun, the IR hits the matrix exactly in the proportion that the filters let through, and which forms a pink or purple color, clogging up all the other color information with its brightness.
If you shoot with a filter on the lens, the proportion of colors is different. For example like this:

I found this picture in the community ru-infrared.livejournal.com
There are also a bunch of pictures taken in the infrared range. The greens on them are white because the BB is exposed just over the foliage.

But why do plants turn out so bright?

In fact, this question is twofold - why does the green look bright and why does the fruit look bright.
Greens are bright because in the infrared part of the spectrum absorption is minimal (and reflection is maximal, which is what the graph shows):

Chlorophyll is to blame for this. Here is its absorption spectrum:

This is most likely due to the fact that the plant protects itself from high-energy radiation, adjusting the absorption spectra in such a way as to obtain energy for existence and not be dried out from too generous sun.

And this is the spectrum of the sun's radiation (more precisely, that part of the solar spectrum that reaches the earth's surface):

Why does the fruit look bright?

Fruit in the skin often does not have chlorophyll, but nevertheless, they reflect IR. Responsible for this substance, which is called epicuticular wax - that very white bloom on cucumbers and plums. By the way, if you google "white bloom on plums", then the results will be anything, but not this.
The sense in this is about the same - it is necessary to preserve the color, which can be critical for survival, and not let the sun dry the fruit while still on the tree. Dried prunes on trees are, of course, excellent, but they do not fit into the life plans of the plant a little.

But damn, why mantis shrimp?

No matter how much I looked, what animals see the infrared range, I came across only mantis shrimps (stomatopods). These are the paws:

By the way, if you do not want to miss the epic with the teapot or want to see all the new posts of our company, you can subscribe to the company page (the "subscribe" button)

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There was an option to buy a cheap VGA resolution digital camera with a viewfinder, but then it would be just one more thing to carry.
Recently at the airport, I tried to turn off the TV with loud chatting of people with my universal TV-Be-Gone controller, but the device didn't work to turn off the TV, so I decided to try to see if it worked or not. I took out my iPhone 4, opened the camera app, pointed the camera at the IR LED TV Be-Gone, and pressed a button on the Be-Gone TV. I didn't see the light from the IR LED in the author's iPhone's viewfinder.
Then it occurred to me to try the front-facing FaceTim camera. I pressed the toggle camera button on the iPhone screen and pointed the camera at FaceTime, the TV-Be-Gone's still flashing IR illumination, and finally I could see the light that was coming out of the IR emitter!
The next steps will repeat the steps above and show you how to see infrared light on your stock iPhone 4, and possibly other smartphones and tablets too.

Step 1. Try using the back of the camera to see the light from the infrared LED

On your iPhone, launch the Camera app, and point the camera at the LED emitters of the TV remote.
When looking at the iPhone screen, press a few buttons on the remote.
Although the remote is likely to emit a bright infrared beam, you cannot see it with your eyes because your eyes are not sensitive to light at the infrared frequency (about 940 nm for a remote).
Your iPhone's main camera cannot see infrared light because Apple added a filter to the lens that blocks infrared light, so infrared rays are not visible on the screen.

Step 2: Now try using the front-facing FaceTime camera to see the light from the infrared LED

Now press the "camera toggle" button - the icon in the upper right corner of the iPhone app's camera so that the screen displays the view from the FaceTime camera, so you'll probably see yourself on the screen.
Now point your FaceTime camera at the LED on your TV remote and press a button on the remote.
Your eye cannot see infrared light, but you will now see infrared light, which appears in the viewfinder as bright white light.
It turns out that the FaceTime camera on the iPhone 4 doesn't have an IR cut filter! Hooray!

Despite the fact that the human eye is capable of perceiving tens of thousands of colors and shades, a person sees the world around him in far from all of its colors and tones, since in addition to visible light, sunlight also contains invisible ultraviolet and infrared rays. However, some living beings in the course of evolution acquired the ability to see in short- (UV) and long-wave (IR) electromagnetic radiation.

Who sees in ultraviolet

To date, scientists have adopted that ultraviolet rays are capable of:

insects and other invertebrates;
many species of birds;
various inhabitants of the underwater world, including fish, molluscs and crustaceans;
reptiles.

Also, some vertebrate inhabitants of the Earth, including mammals, are able to see in UV radiation. For example, dogs and cats, reindeer, and many species of rodents have the ability to see in the ultraviolet spectrum of electromagnetic radiation.

With all this, it is important to note that the ability to see ultraviolet light is not a whim of evolution, but a tool for the survival of living organisms. For example, flying insects use it to find open space for flight, crustaceans to seek shelter, and reptiles and vertebrates to search for food. Bees use their ability to see UV rays to collect nectar from flowers.

Who sees infrared light

Today, science does not know of a single animal capable of seeing infrared light, since to focus such light on the retina, a lens completely different from visible light is needed. Conversely, the eyes of animals, including humans, that can see red light have developed protection against infrared rays, since they would blur the image on the retina.

Sometimes infrared vision is the ability of some animals to celebrate thermal radiation, which occurs due to sensors located on the surface of the upper integument. This ability is inherent in some species of snakes and bats. It is believed that information coming from lukewarm sensors is processed together in the brain along with visual information, so living creatures with heat sensors can see an unfocused image of warm objects.

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